1. Field of the Invention
This invention relates generally to heat engines and refrigeration apparatus that utilize bottoming and topping cycles and binary working fluid, and more particularly to a combined thermodynamic power and cryogenic refrigeration system utilizing a binary working fluid and having a low-temperature bottoming cycle and open or closed modified Brayton topping cycles.
2. Brief Description of the Prior Art
It is known that any system operating on a cycle and receiving heat while doing work must also have a heat-rejection process as part of the cycle. Most prior art systems having thermodynamic cycles require two external heat reservoirs. However, a heat-rejection or heat-recuperation process may be made up in closed cycles with only a single external heat reservoir without a second external heat reservoir, provided that the work medium is a combined mixture of a non-condensable first gas such as helium or hydrogen that possesses high heat capacity and a low-temperature liquid such as liquefied nitrogen, methane, water with antifreeze, etc., wherein the low-temperature liquid is used as an internal cold reservoir to carry out the heat-rejection process and the non-condensable first gas is supercooled during adiabatic expansion producing useful work and serves as coolant to heated liquid recovering from an initial condition of the gas/liquid mixture. Therefore, it is possible to construct a heat engine which will do work and exchange heat with a single external heat reservoir. The conversion of the heat energy into another form is appreciably enhanced by employing a binary working fluid in the low temperature closed bottoming cycle for cooling of the working fluid of the open or closed topping before its compression or during the multistage compression with intercooling. Thus, if the closed topping cycle utilizes the cool ambient air as a heat source, it gets cooler and the producing power may be converted into heat by means of a heat pump. The present system is distinguished over the prior art in that in the present system, a portion of the cool air becomes cooler heating another portion of air simultaneously.
Heat engines are known in the art which have combined cycles such as a combination of Brayton and Rankin cycles.
Fruschi, U.S. Pat. No. 5,386,685 discloses a method and apparatus for a combined cycle power plant. Simpkin, U.S. Pat. No. 5,431,016 discloses a high efficiency power generation engine.
One of the principal shortcomings of these combined cycle systems is that they are not capable of cooling air during its compression in the topping Brayton cycle.
The present system utilizes a low-temperature closed bottoming cycle that provides deep cooling of the working fluid of a modified Brayton closed or open topping cycle. In the preferred embodiment of the present system, the low-temperature bottoming cycle utilizes the apparatus shown and described in our commonly-owned U.S. patent Ser. No. 08/929,294, which is hereby incorporated herein by reference. This incorporation-by-reference is for the purpose of simplifying the drawings and descriptions of this invention and, also for the purpose of providing a clear and concise description of this invention.